/Engine/Source/Runtime/Engine/Classes/GameFramework/HUD.h
returns false if selection could not occur. Make sure template class is extendingAActor.
OutActors The actors that are within the selection box according to selection rule
template<typename ClassFilter> bool GetActorsInSelectionRectangle ( const FVector2D & FirstPoint, const FVector2D & SecondPoint, [TArray](API\Runtime\Core\Containers\TArray)< ClassFilter * > & OutActors, bool bIncludeNonCollidingComponents, bool bActorMustBeFullyEnclosed )